Overhand serving is a little trickier than underhand serving, more power and strength, but it does get you a lot more points. You can do it in one spot or you could step pretty far away from the line so that you wouldn't step over the line. You have one leg in front of the other, you hold your oppisite hand out in front of you sort of outto your face, your dominant hand starts at your side and while the volleyball gets back to your face after you throw it in the air, you rise your arm and hit the ball sort of toward the grown, but make sure you throw the ball sort of in front of you so you can step up and and then hit the ball, use all your power and hit the ball!
Underhand serving is much easier especially if you're first starting out, but if you're up for a challenge try overhand serving. You're oppisite hand should be flat because that's the hand you hold the ball in, it should be out in front of your dominant arm, that arm should be in a fist becuase you're going to be hitting the volleyball with it. You swing you're dominant arm back and then swing it back forward so you can hit the ball, but just before you hit the ball you should drop the ball and then hit it with all your power, but make sure that the volleyball doesn't go out of bounds!